Lamp and lighting unit with interference coating and blocking device for improved uniformity of color temperature

ABSTRACT

The invention relates to a non-automotive-headlight lamp ( 1 ) comprising a lighting element ( 3 ) and a transparent bulb ( 2 ), which is at least partly equipped with an interference coating ( 4 ) for e.g. changing the color or color temperature of the lamp ( 1 ), and to a lighting unit ( 15 ) comprising such a lamp ( 1 ) being mounted in a reflector ( 12 ). But the invention is also related to lighting units ( 15 ) where the interference coating ( 4 ) is not applied to the lamp ( 1 ) but to the reflector ( 12 ). In these lamps ( 1 ) or lighting units ( 15 ) light components ( 8 ) not appropriately filtered by the interference coating ( 4 ) lead to undesired wavelengths in the illumination beam and/or to a compromised color uniformity of the beam. Such light components ( 8 ) may stem from missing or insufficient filters on part of the lamp ( 1 ), from non-normal incidence of the rays ( 8 ) on the filter ( 4 ), and, in reflectors ( 12 ) with interference coating ( 4 ), from direct light ( 8 ) not hitting the reflector ( 12 ). The invention adds a blocking device ( 5, 6, 7 ) to the lamp ( 1 ) or lighting unit ( 15 ) to substantially prevent these light components ( 8 ) to enter the illumination beam. Whereas constructively similar blocking devices ( 5, 6, 7 ) are known from automotive headlight lamps for preventing glare their benefits in the context of interference coatings ( 4 ) were overlooked in the prior art.

The invention relates to a lamp comprising a lighting element and atransparent bulb, which is at least partly equipped with an interferencecoating. Such interference coatings are e.g. used for changing the colorappearance of the lamp or for raising its color temperature. Such lampscan, among other things, be mounted in a reflector, and the thusobtained lighting unit may serve for various lighting applications, e.g.shop, home, accent, spot, or theater lighting. Thus, the inventionencompasses such lighting units comprising a reflector and an inventivelamp, too.

But the invention also relates to a lighting unit comprising a reflectorand a lamp, wherein the reflector is equipped with an interferencecoating. These lighting units are an alternative for the firstlymentioned lighting unit, in which the lamp carried the interferencecoating. Accordingly, both embodiments of such units can be used forsimilar purposes. Moreover, lamps with an interference coating might beused in reflectors with an interference coating, too, these interferencecoatings supplementing each other. E.g., the lamp's interference coatingmight transmit only the wavelengths below the blue whereas thereflector's coating might transmit the infrared while reflecting thevisible, thus in combination yielding a yellow “cold” light, colddenoting the absence of the infrared.

DE 86 00 642 U1 discloses a lamp carrying an interference coating forchanging the lamp's color. The coating is made of alternative ¼λ-layersof a material with relatively low and a material with relatively highrefraction index, and can be produced e.g. by vapor deposition or bydipping. The document further discloses several filter designs usefulfor obtaining a yellow lamp. This color filtering can be furtherimproved by supplementing the interference coating with an additionalwavelength-selective absorption filter e.g. made of one or two layers ofFe2O3, Sr2O3, CoO, or CuO, which are preferably separated from theinterference coating by an adaptation layer with a relatively lowrefraction index. In order to avoid a further reciting of thisdocument's disclosure DE 86 00 642 U1 in its entirety is included byreference in this application. Besides the above materials for theadditional wavelength-selective absorption filter cited in DE 86 00 642U 1 other materials can be used as e.g. CoA12 O4.

DE 86 00 642 U1 mentions on p. 2, lines 23-38 that in certainembodiments light generated by the lighting element of the lamp mayimpinge on the bulb's interference coating at a considerably largenon-normal incidence. This e.g. might occur with relatively long bulbs.Such non-normal incidence has the effect that wavelengths, which shouldbe reflected back into the lamp by the interference coating, are partlytransmitted, thus influencing the lamp's color appearance. But DE 86 00642 U1, concentrating on automotive headlight lamps, terms this effectas small and points out that the usage of an additionalwavelength-selective absorption filter removes the effect.

EP 0 986 093 A1 re-addresses the problems caused by such non-normalincidence on the interference coating. Whereas also EP 0 986 093 A1terms this a minor problem for automotive headlight lamps (in column 1,lines 26-30), it points out that lamps in other applications as e.g. forautomotive stop lights or beacons have a different construction as e.g.a pear-shaped bulb. In such lamps, the effect of non-normal incidence isnot negligible but might e.g. cause the lamp appear in different colorsat different viewing angles respectively might cause the lamp generatecolored lighting patterns on the illuminated object area.

To solve these problems EP 0 986 093 A1 refers to the method disclosedin EP 0 460 913 A2 of using a locally varying thickness of theinterference coatings of the lamp and of the reflector the lamp ismounted into to avoid ring-shaped colored lighting patterns. EP 0 986093 A1 then further develops this method by giving prescriptions on howto determine the local thickness of the interference coating. Again, toavoid further reciting the disclosure of EP 0 986 093 A1, as e.g.concerning concrete filter embodiments and production methods, thisdocument in its entirety is included by reference in this application.

Whereas varying the local thickness of an interference coating accordingto EP 0 986 093 A1 offers a solution to the problems caused bynon-normal incidence this method causes a considerable increase inproduction complexity and costs. Moreover, due to production constraintsthere may be parts of the lamp's bulb that carry no or only aninsufficient interference coating leading to not or at leastinsufficiently filtered light components. E.g., the pinch part of thebulb might be sandblasted after the interference coating was applied,such sandblasting removing the interference coating on the pinch. In thesame way, on strongly curved parts of the bulb the interference might bebadly defined, e.g. in the transition region between pinch and middlepart of the bulb or at the top of a single-ended lamp. In this latercase, of course, also the problem of non-normal incidence arisesconcurrently. In a lighting unit, in which the reflector carries aninterference coating the light directly leaving the lighting unit, i.e.the light generated by the lighting element of the lamp and directedtowards the open end of the reflector, is not filtered by thisinterference coating and thus adds undesired wavelengths in the lightingunit's beam.

All these phenomena of non-normal incidence, missing or badly definedinterference coatings, and direct light have in common that lightcomponents not having been appropriately filtered by the interferencecoating appear in the illumination beam. Such components lead toundesired wavelengths in the illumination beam and/or compromise theillumination beam's color uniformity.

It is therefore an object of the invention to provide, in the realm ofnon-automotive-headlight lamps and in the realm of reflector lightingunits, a simple and cheap solution at least alleviating to a largeextent the problems of undesired wavelengths and insufficient coloruniformity caused by inappropriately filtered light components in theillumination beam.

The first object is achieved by a non-automotive-headlight lampcomprising

a transparent bulb,

a lighting element inside the bulb,

an interference coating on at least part of the bulb, and

a blocking device being designed for blocking at least part of the raysgenerated by the lighting element and not appropriately filtered by theinterference coating (4).

The term “non-automotive-headlight” is used in the sense of a disclaimerfor establishing novelty over the prior art, i.e. a“non-automotive-headlight lamp” denotes any lamp with the exception of alamp constructed for use in a car headlight.

As already pointed out in the introductory section such a lamp might bemounted in a reflector to form a lighting unit. Thus, the invention alsorelates to a lighting unit comprising

a reflector, and

a non-automotive-headlight lamp according to claim 1 mounted within thereflector.

In such a lighting unit, the blocking device might be constructed not asa part of the lamp but as a separate shield. Accordingly, the inventionadditionally encompasses a non-automotive-headlight lighting unitcomprising

a reflector,

a shield,

a lamp mounted within the reflector, the lamp comprising

a transparent bulb,

a lighting element inside the bulb, and

an interference coating on at least part of the bulb, wherein the shieldis designed for absorbing at least part of the rays generated by thelighting element and not appropriately filtered by the interferencecoating (4).

Moreover, as also pointed out in the introductory section, instead ofcoating the lamp with an interference filter the reflector might becoated. Therefore, the second object of the invention is achieved by alighting unit comprising

a reflector with an interference coating,

a lamp mounted within the reflector, and

a blocking device being designed for blocking at least part of the raysgenerated by the lamp and being directed to the open end of thereflector.

Of course, as is obvious to the skilled man and e.g. mentioned in EP 0986 093 A1, lamp and reflector interference coatings might be combinedin one lighting unit.

Thus, the invention relies on the insight that a simple and costefficient solution for at least alleviating to a large extent theproblems caused by inappropriately filtered light components consists inblocking these light components from reaching the illumination area.I.e., that part of the light is blocked, which otherwise would not passany interference filter, would only pass an insufficient filter, orwould pass the filter at non-normal incidence.

It has to be pointed out that lamps, which carry an interference coatingon their bulbs and possess a non-transparent coating on their top, arewell known for automotive-headlight applications. E.g., the lamp shownin the figure of DE 86 00 642 U1 and discussed therein is of such atype. The document explicitly mentions on p. 4, lines 10-16 that thelamp is thought to be mounted in a reflector for generating a low beam(“Abblendbündel”) and a high beam (“Hauptbündel”), which clearlyclassifies the lamp for the use in an automotive headlight. Furthermore,as a specific example, the document mentions a yellowH4-automotive-lamp.

But the existence of these prior-art automotive headlight lamps has tobe clearly distinguished from the invention at issue: Thenon-transparent coatings on the tops of automotive headlight lamps,usually termed as bulb, capsule, or black caps, serve the sole purposeof regulating the luminance of the headlight in order to prevent glaringthe other traffic participants by the direct light of the lamp'slighting element. These caps were known prior to the introduction ofinterference coatings and the art prior to the invention at issue didnot recognize the beneficial effects of such blocking devices for theclaimed purposes of reducing inappropriately filtered light componentsof an interference-coated lamp or lighting unit.

That the prior art actually overlooked the claimed beneficial effects ise.g. obvious from the already cited passages of DE 86 00 642 U1 and EP 0986 093 A1 terming the problems caused by non-normal incidence small orminor for automotive headlight lamps and from the fact that EP 0 986 093A1, while knowing about the caps of automotive headlight lamps,developed another solution for this problem, i.e. developed further theidea of a locally varying thickness of the interference coating.

An inventive lamp might be a light source of any kind, i.e. encompasseshalogen lamps as well as discharge lamps and might further compriseother light sources, too, e.g. ones utilizing chemical effects, the onlyprerequisite being that the light source emits a light 'spectrum, whichcan be usefully filtered by an interference coating. Accordingly, aninventive lamp's lighting element denotes that part of the lamp emittingthe light thought to be filtered by the interference coating, e.g. thefilament of an incandescent lamp, the arc of a high-pressure dischargelamp, or the phosphors converting the ultraviolet light generated in afluorescent lamp.

An interference coating on the bulb of an inventive lamp or on areflector may be of any type transmitting one part of the spectrum andreflecting the other. The design and production of such filters isnowadays state-of-the-art and examples of filters transmitting thewavelengths in the yellow, the orange, or the red are given e.g. in DE86 00 642 U1 or EP 0 986 093 A1. But besides changing the color of alamp such interference coatings might as well be designed for making thelamp more daylight like, i.e. for raising its color temperature, or forincreasing their energy efficiency respectively at least partly avoidingundesired heating of the illumination area by reflecting back theinfrared into the lamp. The later effect, i.e. obtaining “cold” lightcan also be obtained by coating the reflector the lamp is mounted intoand having this reflector transmit the infrared while reflecting thevisible.

The blocking device might perform its function by absorbing orreflecting the light impinging on it or by a mixture thereof. Reflectionoffers the advantage of increasing the efficiency of the lamp orlighting unit: In an incandescent lamp, the reflected light at leastpartially heats the filament. In a lighting unit whose reflector carriesan interference coating, the light reflected by the blocking device hitsthe reflector and its interference coating and thus contributes to alarge extent to the illumination beam.

The blocking device might e.g. be realized as a shield, mounted as partof the lamp or as a separate element, a cap, e.g. made of an absorbingor mirroring metal and mounted on the bulb, covering part of it, or as anon-transparent coating on part of the bulb, e.g. of the same type asknown from the automotive headlight lamps, e.g. a black cap made ofstandard silicon iron oxide black. In principle, the blocking could alsobe achieved by using a non-transparend material for the bulb at theappropriate positions, e.g. manufacturing the bulb's ends of anon-transparent material, using a transparent one only for the bulb'smiddle part.

The blocking device is to be provided at a position where it blocks atleast part of the light, which contains the inappropriately filteredlight components. Thus, for blocking the direct light of a lamp beingmounted in a reflector it has to block the light being directed from thelighting element to the reflector opening. In this way, besidessuppressing inappropriately filtered light components, the blockingdevice at the same time serves the purpose of preventing glare from thisdirect light.

The problems of non-normal incidence are e.g. prominent with longlighting elements being mounted transversely to the lamp's axis ofcylindrical symmetry, with elongated bulb forms as well as with bentbulb shapes. Common examples are low-voltage halogen lamps for homelighting. These lamps are single-ended, i.e. their electrical contactsleave the lamp on one side, whereas at the opposing side the lamps'walls terminate in a concave rounding and finally in a convex top,necessarily leading to considerable non-normal incidence of the lightingelement's light, and additionally showing the problems of a badlydefined interference coating on the strongly curved parts of the bulb'stop. An effective blocking element according to the invention for such alamp consists in a non-transparent coating or a cap covering the lamp'stop, i.e. their end opposing the electrical contacts.

While the above aspects of the invention have mostly been discussed inisolation it is obvious to the skilled man that they may also be used incombination as well as being combined with further measures. E.g.,interference coatings in a lighting unit may be employed on the lamp aswell as on the reflector, the lamp's coating transmitting wavelengthsbelow the blue and the reflector's coating transmitting the infrared,thus in combination yielding a yellow “cold” light. Furthermore,additional wavelength-selective absorption coatings may assist theinterference coatings as e.g. disclosed in DE 86 00 642 U1.

Inventive lighting units may be designed for various applications,dependent on the type of the lamp and the filter curve of theinterference coating. Some of the envisaged applications are shoplighting, home lighting, accent lighting, spot lighting, theaterlighting, fiber-optics applications, and projection systems in general.

These and further aspects and advantages of the invention will befurther illustrated by the embodiments and, in particular, by thedescription of the attached figures.

FIGS. 1 to 3 show sectional views of embodiments of an inventivenon-automotive-headlight lamp.

FIGS. 4 and 5 show sectional views of embodiments of an inventivelighting unit.

FIG. 1 shows a first embodiment of an inventive non-automotive-headlightlamp 1, in which the parts most relevant for the invention are equippedwith reference numerals and exemplary dimensions are given inmillimeters partly together with their tolerances. But lamp 1 might aswell be manufactured with differing dimensions. Lamp 1 is a single-endedhalogen incandescent lamp, which can e.g. be inserted into a reflectorand used for shop or home lighting. It is operated at a voltage of 12 Vwith a power of 50 W but might as well be designed to being operated atother low voltages as e.g. 6 V and 24 V or might also be designed formains voltages as e.g. 110 V and 220 V. Single-ended means that bothelectrical contacts 21 leave lamp 1 on one side only. The side opposedis termed as the top 22 of lamp 1. Lamp 1 further comprises alight-transparent bulb 2, which is coated on its outer side with aninterference coating 4, indicated in FIG. 1 by a dashed line. Thelighting element 3 of lamp 1 is a tungsten filament formed as a coil.

Caused by its production process, the top 22 of bulb 2 consists ofseveral concave and convex parts, necessarily leading to considerablenon-normal incidence of the lighting element's light. To block thislight from leaving lamp 1 top 22 is coated on the outside ofinterference coating 4 by a non-transparent coating 5 functioning as ablocking device, which might be produced e.g. by a dipping or sputteringprocess. Coating 5 might e.g. consist of standard silicon iron oxideblack absorbing the light impinging on it as well as might beconstructed as a mirror reflecting the impinging light back into lamp 1.Of course, as interference coating 4 has no function on top 22 it mightthere be omitted completely or non-transparent coating 5 might beprovided between bulb 2 and interference coating 4, whichever is moresuitable for the production process at hand.

But in case of a reflective coating 5 as blocking device it is moreadvantageous to provide reflective coating 5 beneath interferencecoating 4 or to omit interference coating 4. In this case part of thelight being reflected by reflective coating 5 is re-absorbed at filament3, thus heating filament 3 and saving some energy input to lamp 1.Moreover, dependent on the lamp's geometry, some other part of the lightbeing reflected by reflective coating 5 can leave lamp 1 at anotherplace of bulb 2 passing there interference coating 4 at substantiallynormal incidence. But in this latter case care has to be taken that nottoo much reflected light leaves lamp 1 at positions where it passesinterference coating 1 at non-normal incidence.

FIG. 2 shows a second embodiment of an inventivenon-automotive-headlight lamp, which coincides with FIG. 1 with theexception that the blocking device is formed as a non-transparent cap 6.Cap 6 can e.g. be mechanically attached to bulb 2 by pressing it intoclose contact to bulb 2 or can be glued to bulb 2. For illustration,FIG. 2 shows two light rays 8 being generated by lighting element 3 andhitting interference coating 4 at non-normal incidence. Exemplifying,one of rays 8, i.e. ray 9, is drawn as being absorbed by a black,absorbing cap 6, while the other of rays 8, i.e. ray 10, is drawn asbeing reflected by a reflecting, e.g. mirror covered cap 6.

FIG. 3 shows a third embodiment of an inventive non-automotive-headlightlamp, which shows a two-ended incandescent lamp 1 with bulb 2,electrical contacts 21, filament 3 as lighting element, and interferencecoating 4 on the middle part of the bulb 2. In some production processeswill the outer, pinched parts of the bulb 2 be sandblasted whichsandblasting destroys a possible prior interference coating on theseouter parts. In order to avoid unfiltered light to leave lamp 1 viathese outer parts they have been coated by an absorption coating 5 asblocking device. Thus, ray 8 from filament 3 otherwise leaving lamp 1and adding an undesired component to the illumination beam now will beabsorbed by blocking device 5. Of course, if lamp 1 is to be used withina reflector the pinched part of bulb 2 inserted into the reflector'sneck need not be coated with absorption coating 5 as the light directedto that part will be absorbed within the reflector's neck anyhow.

FIG. 4 shows a first embodiment of an inventive lighting unit 15 withexemplary dimensions given in millimeters. A lamp is mounted within areflector 12, which carries on its inner side an interference coating 4,shown as a dotted line. The reference numerals 21 denote the lampselectrical contacts, 2 its bulb, and 3 its lighting element. A shield 7,fixed by plates 13 to the reflector 12, serves as a blocking element forthe light of the lighting element 3 being directed to the open end ofreflector 12. For illustration, one of these light rays 8 is shown,impinging on shield 7 and being absorbed there. The light 11 of lightingelement 3 being directed to the inner side of reflector 12 is reflectedthere into the reflector's main beam while being filtered byinterference coating 4.

FIG. 5 shows a second embodiment of an inventive lighting unit 15, againshowing a lamp being mounted in a reflector 12, the reflector 12carrying on its inner side an interference coating 4. But whereas inFIG. 4 a one-sided incandescent lamp was used FIG. 5 shows a two-sidedhigh-pressure gas discharge lamp, whose electrical contacts 21 are leadto the rear side of reflector 12. The lighting element 3 is now realizedas an arc 3 burning between the electrodes 23 inside the bulb 2 of thegas discharge lamp. Now, a reflecting coating 5 on the middle part ofbulb 2 and an absorbing coating 5′ on the outer, pinchec part of bulb 2,both parts being directed to the open side of reflector 12, block thedirect light of lighting element 3. Thus, not just the light rays 11being directed from arc 3 to reflector 12 form the illumination beam butalso the light rays 8, after reflection at reflection coating 5, hitreflector 12 passing its interference coating 4 and contribute as rays11′ to the illumination beam. Rays being directed from arc 3 to theouter, pinched part of bulb 2 at the reflector's open side, whichotherwise would add undesired wavelengths to the illumination beam, areabsorbed by absorbing coating 5′.

In the situations of FIGS. 4 and 5 where the reflector 12 carries theinterference filter 4 it might be advantageous to equip the bulb 2 ofthe lamp with an additional filter that in itself might be aninterference filter, too. E.g., if the interference filter 4 ofreflector 12 is designed for raising the color temperature of thereflected light, e.g. to make it more daylight like, bulb 2 of the lampcan be provided with an infrared reflecting (IR) interference filter.Such an IR filter will reflect the infrared back into the lamp acting asadditional energy source heating filament 3 of an incandescent lamp orthe discharge of a discharge lamp thus saving some of the energy inputto the lamp.

1. A non-automotive-headlight lamp comprising: a transparent bulb, alighting element inside the bulb, the lighting element configured togenerate light rays, an interference coating on at least part of thebulb, and a blocking device coupled to the bulb and configured to blockat least part of the rays (i) generated by the lighting element and (ii)not appropriately filtered by the interference coating, wherein theblocking device blocks by absorption of a part and reflection of aremaining part of the rays impinging on the blocking device.
 2. Anon-automotive-headlight lamp according to claim 1, wherein the lamp isadapted to be mounted in a reflector having an open end, and theblocking device is further configured to block at least part of the raysgenerated by the lighting element and being directed to the open end ofthe reflector.
 3. A non-automotive-headlight lamp according to claim 2wherein the lamp is double-ended, and the blocking device comprises anabsorbing coating covering an outer pinched portion of the bulb of thelamp, and a reflective coating on a middle portion of the bulb of thelamp, both the absorbing coating and the reflective coating beingdirected to the open end of the reflector.
 4. A non-automotive-headlightlamp according to claim 1, wherein the interference coating is furtherconfigured to raise the color temperature of the light emitted by thelighting element, and/or change the color of the light emitted by thelighting element.
 5. A non-automotive-headlight lamp according to claim1, wherein the lamp comprises an additional wavelength-selectiveabsorption coating adapted to support the filtering characteristics ofthe interference coating.
 6. A lighting unit comprising a reflector, anda non-automotive-headlight lamp according to claim 1 mounted within thereflector.
 7. A lighting unit according to claim 6 the lighting unitfurther being configured to be used in one of the followingapplications: shop lighting, home lighting, accent lighting, spotlighting, theater lighting, fiber-optics applications, and projectionsystems.
 8. A non-automotive-headlight lighting unit comprising areflector, a shield coupled to the reflector, a lamp mounted within thereflector, the lamp comprising a transparent bulb, a lighting elementinside the bulb the lighting element configured to generate light rays,and an interference coating on at least part of the bulb, wherein theshield is configured to block at least part of the rays (i) generated bythe lighting element and (ii) not appropriately filtered by theinterference coating.
 9. A lighting unit comprising a reflector with aninterference coating, the reflector including an open end, a lampmounted within the reflector, the lamp configured to generate lightrays, and a blocking device (i) configured to block at least part of therays generated by the lamp and (ii) being directed to the open end ofthe reflector, wherein the blocking device is configured to block byabsorption of a part and reflection of a remaining part of the raysimpinging on the blocking device.